Y-doped TaON films were grown on (001)YSZ and (012)Al2O3 substrates by radio frequency (RF) magnetron reactive sputtering deposition from Ta metal target and Y metal chips under the mixture gases of N2, O2 and Ar gases. Films with various Y content were prepared by changing area ratio of Y/(Y + Ta) of the target. The pure monoclinic phase was obtained for TaON films on both substrates by controlling the partial pressure of N2 and O2 gasses. Crystal structure changed from the monoclinic phase to the orthorhombic one with the lattice parameters of a = 0.518 nm, b = 0.488 nm, and c = 0.504 nm with the increase in Y content in the films. Our results reveal that TaON could be used as a novel mother fluorite-like monoclinic structure to prepare orthorhombic phase.